1. Field of the Invention
This invention is related in general to construction materials and, in particular, to a process for manufacturing an aggregate of cement and particulate porous-rock material.
2. Description of the Prior Art
Cement is used to bind particulate matter, such as sand and gravel, in order to produce strong composites used routinely in the construction of buildings and other structures. In particular, cement is also combined with various kinds of porous rocks, like volcanic cinder, scoria and pumice, to produce light-weight composites that can be used advantageously for applications where weight and thermal insulating properties are considered important. Because of the porous nature of the rock, the resulting composite tends to be lighter and, for some applications, more practical than conventional concrete for construction purposes. In addition, the interstitial voids in the rock provide an insulating barrier to thermal conductivity that makes the composite less sensitive to and more stable under normal thermal expansion cycles. These advantages render these types of aggregates particularly attractive as construction material in arid and hot climates.
The universal and conventional way of preparing these composite materials consists of mixing the rock particles and the cement in essentially dry conditions in a batch reactor and then gradually adding an amount of water sufficient to reach the desired degree of hydration, full hydration being the preferred objective. As one skilled in the art would readily recognize, the percentages of each component may be varied within allowable ranges to change the texture, fluidity and/or other characteristics of the resulting slurry. The structural strength of the composite produced by forming the slurry is a function of its composition and the conditions under which the hydration and curing stages of the cement are carried out.
One common problem of light-weight composites produced from porous rock particles and cement with respect to conventional concrete structures is their lower compressive strength, which limits the applications for which they can be used in spite of the desirability of their thermal properties and lower weight. Accordingly, there is still a need for a stronger, light-weight composite produced from cement and porous rock. This disclosure is directed at an improved, novel process for manufacturing such aggregate materials.
One objective of this invention is a process for making cement/porous-rock aggregates that have greater compressive strength than found in similar composites manufactured by conventional mixing processes.
Another objective is a process that results in a composite with improved thermal insulating properties.
Another goal of the invention is a method of manufacture of cement/porous-rock composites that is suitable for continuous mixing.
Still another goal is a process that is particularly useful with scoria, cinder and bottom ash.
Another object is a process that is also particularly suitable for producing concretes made with scoria, cinder and bottom ash having low slump characteristics immediately prior to placement.
A final objective is a process that can be implemented easily and economically with commercially available materials and manufacturing equipment, modified only to the extent necessary to fit the requirements of the invention.
Therefore, according to these and other objectives, the present invention consists of a process for binding porous-rock particles with cement, wherein the rock is saturated in water prior to mixing with the cement powder. The saturation step causes water to fill the voids in the porous structure of the rock such that, during mixing of the wet rock with cement, cement particles adhere to the surface of the rock and are mostly precluded from reaching void spaces in the rock. As a result of this procedure, the interstitial water is available from within the rock for the cement hydration process, thereby providing a more uniform curing step than otherwise available, and a greater proportion of the cement is appropriately placed on the outer surface of the particles for bonding. The resulting aggregate is stronger than obtained by conventional mixing processes. In addition, because of the voids left in the composite after the cement has cured and the interstitial water has been either used by the hydration process or has evaporated, the material also exhibits improved insulating properties.